1. Field of the Invention
The present invention is broadly concerned with novel substantially biodegradable and substantially water soluble anionic polymers and derivatives thereof which have significant utility in agricultural applications, especially plant nutrition and related areas. More particularly, the invention is concerned with such polymers, as well as methods of synthesis and use thereof, wherein the preferred polymers have significant levels of anionic groups. The most preferred polymers of the invention include recurring polymeric subunits made up of dicarboxylic (e.g., maleic acid or anhydride, itaconic acid or anhydride, and other derivatives thereof) monomers. The polymers may be applied directly to the ground adjacent growing plants, complexed onto ions, applied directly to seeds, and/or mixed with or coated with phosphate-based fertilizers to provide improved plant nutrition products.
2. Description of the Prior Art
Lignosulfonates, polyacrylates, polyaspartates and related compounds have become known to the art of agriculture as materials that facilitate nutrient absorption. All of them suffer from significant disadvantages, which decrease their utility in comparison to the art discussed herein and limit performance.
Lignosulfonates are a byproduct of paper pulping; they are derived from highly variable sources. They are subject to large, unpredictable variations in color, physical properties, and performance in application areas of interest for this invention.
Polyacrylates and polymers containing appreciable levels thereof can be prepared with good control over their composition and performance. They are stable to pH variations. However, polyacrylates have just one carboxylate per repeat unit and they suffer from a very significant limitation in use, namely that they are not biodegradable. As a result, their utility for addressing the problems remedied by the instant invention is low.
Polyaspartates are biodegradable, but are very expensive, and are not stable outside a relatively small pH range of about 7 to about 10. They usually have very high color, and incorporate amide groups, which causes difficulties in formulating them. Additionally, polyaspartates have just one carboxylate per repeat unit and are therefore not a part of the present invention.
Preparation of itaconic Acid homopolymers has been known to the art of polymer chemistry for an extended period of time. Several approaches to making it exist. One approach is by the direct polymerization of itaconic acid and/or its salts in aqueous or organic solutions under a wide range of conditions. Such reactions are described in the Journal of Organic Chemistry, Vol. 24, pg. 599 (1959) the teachings of which are incorporated by reference herein. Another approach is to begin with esters of itaconic acid, polymerize them under suitable conditions, and then hydrolyze the ester groups off in order to liberate polyitaconic acid. This approach is described in U.S. Pat. No. 3,055,873, the teachings of which are hereby incorporated by reference. Additionally, a very good summary of many aspects of the prior art is found in U.S. Pat. No. 5,223,592, the teachings of which are hereby incorporated by reference.
It will thus be seen that the prior art fails to disclose or provide polymers which can be synthesized using a variety of monomers and techniques in order to yield end products which are substantially biodegradable, substantially water soluble, and have wide applicability for agricultural uses. Moreover, no prior art or combination of prior art discloses preparation of itaconic acid copolymers with one or more organic acids containing at least one olefinic bond and at least two carboxylic acid groups. Furthermore, while the prior art does disclose a variety of methods for making polyitaconic acid homopolymer, it fails to teach, disclose, or suggest the utility such materials unexpectedly have for a wide variety of agricultural uses.